"""Bounded, ephemeral H.264 playback; original recordings remain untouched."""
from contextlib import contextmanager
import http.client
import os
import shutil
import subprocess
import threading
import tempfile
import time
import urllib.request
from pathlib import Path

SLOTS = threading.BoundedSemaphore(2)
MAX_SOURCE_BYTES = 256 * 1024 * 1024
MAX_SESSION_SECONDS = 300


class PlaybackError(Exception):
    pass


@contextmanager
def cached_source(source, authorization, reserve_bytes):
    # A private, bounded scratch file decouples MediaMTX's HTTP write timeout
    # from browser buffering and pause. Use the data disk, not a small /tmp RAM disk.
    base = Path(os.environ.get('VISION_DATA', tempfile.gettempdir())) / 'playback-tmp'
    base.mkdir(mode=0o700, parents=True, exist_ok=True)
    for old in base.glob('buffer-*'):
        try:
            if old.is_symlink() or not old.is_dir() or time.time() - old.stat().st_mtime < 3600:
                continue
            (old / 'source.mp4').unlink(missing_ok=True)
            old.rmdir()
        except OSError:
            pass
    with tempfile.TemporaryDirectory(prefix='buffer-', dir=base) as folder:
        if shutil.disk_usage(folder).free < reserve_bytes + MAX_SOURCE_BYTES:
            raise PlaybackError('磁盘剩余空间不足以缓冲回放，请先释放空间')
        request = urllib.request.Request(source, headers={'Authorization': authorization})
        target = Path(folder) / 'source.mp4'
        deadline = time.monotonic() + 30
        size = 0
        with urllib.request.urlopen(request, timeout=10) as response, target.open('wb') as output:
            while chunk := response.read(256 * 1024):
                size += len(chunk)
                if size > MAX_SOURCE_BYTES:
                    raise PlaybackError('该录像片段过大，请缩短回放时段')
                if time.monotonic() > deadline:
                    raise PlaybackError('回放缓冲超时，请稍后重试')
                if shutil.disk_usage(folder).free < reserve_bytes + len(chunk):
                    raise PlaybackError('磁盘预留空间不足，已停止缓冲回放')
                output.write(chunk)
        if not size:
            raise PlaybackError('该时段没有可读取的录像')
        yield str(target)


def command(source, authorization, duration):
    executable = shutil.which('ffmpeg')
    if not executable:
        raise PlaybackError('回放转换需要服务器安装 FFmpeg')
    device = os.environ.get('VISION_VAAPI_DEVICE', '/dev/dri/renderD128')
    acceleration = []
    if os.access(device, os.R_OK | os.W_OK):
        acceleration = ['-hwaccel', 'vaapi', '-hwaccel_device', device,
                        '-hwaccel_output_format', 'vaapi', '-extra_hw_frames', '8']
        video = ['-vf', 'fps=15,scale_vaapi=w=1920:h=1080:format=nv12:force_original_aspect_ratio=decrease:force_divisible_by=2',
                 '-c:v', 'h264_vaapi', '-profile:v', 'main', '-level:v', '4.1',
                 '-rc_mode', 'CQP', '-qp', '25', '-g', '30', '-bf', '0']
    else:
        video = ['-vf', 'fps=10,scale=768:432:force_original_aspect_ratio=decrease:force_divisible_by=2',
                 '-c:v', 'libx264', '-threads', '1', '-preset', 'veryfast',
                 '-tune', 'zerolatency', '-profile:v', 'baseline', '-pix_fmt', 'yuv420p',
                 '-crf', '26', '-g', '20', '-bf', '0']
    input_options = (['-rw_timeout', '15000000', '-headers', 'Authorization: ' + authorization + '\r\n']
                     if authorization else [])
    return [executable, '-hide_banner', '-loglevel', 'error', '-nostdin',
            '-threads', '1', '-filter_threads', '1'] + acceleration + input_options + [
            '-analyzeduration', '1000000', '-probesize', '1000000',
            # Recordings are finite HTTP downloads. Pacing their input like a
            # live source stalls upstream writes and truncates long responses.
            '-i', source, '-t', str(duration),
            '-map', '0:v:0', '-map', '0:a:0?', '-sn', '-dn'] + video + [
            '-c:a', 'aac', '-ar', '48000', '-ac', '1', '-b:a', '64k',
            '-movflags', '+frag_keyframe+empty_moov+default_base_moof',
            '-frag_duration', '1000000', '-f', 'mp4', 'pipe:1']


@contextmanager
def stream(source, authorization, duration, reserve_bytes=8 * 1024**3):
    if not 0 < duration <= MAX_SESSION_SECONDS:
        raise PlaybackError('请刷新页面，使用每段最多 5 分钟的自动连续回放')
    if not SLOTS.acquire(blocking=False):
        raise PlaybackError('已有两个回放正在进行，请关闭其他回放后重试')
    process = timer = None
    try:
        if not shutil.which('ffmpeg'):
            raise PlaybackError('回放转换需要服务器安装 FFmpeg')
        with cached_source(source, authorization, reserve_bytes) as local_source:
            # Credentials never appear in the converter's process arguments.
            process = subprocess.Popen(command(local_source, '', duration),
                                       stdin=subprocess.DEVNULL, stdout=subprocess.PIPE,
                                       stderr=subprocess.DEVNULL)
            timer = threading.Timer(duration + 45, process.kill)
            timer.daemon = True
            timer.start()
            try:
                yield process.stdout
            finally:
                if process.poll() is None:
                    process.terminate()
                    try:
                        process.wait(timeout=3)
                    except subprocess.TimeoutExpired:
                        process.kill()
                        process.wait()
    except (OSError, http.client.HTTPException) as exc:
        raise PlaybackError('录像转换服务暂不可用') from exc
    finally:
        if timer:
            timer.cancel()
        if process:
            if process.poll() is None:
                process.terminate()
                try:
                    process.wait(timeout=3)
                except subprocess.TimeoutExpired:
                    process.kill()
                    process.wait()
            process.stdout.close()
        SLOTS.release()